1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle which is propelled by a plurality of sources for drive power, and more particularly relates to such a control device which improves fuel consumption.
2. Description of the Related Art
A control device for a hybrid vehicle is known (refer to Japanese Laid-Open Patent Publication No. H8-126116) which is constituted so as to obtain information related to the route of travel from a navigation device, and so as to set the operational point for an internal combustion engine and an electric motor by setting a target value for battery remaining amount according to the route to be travelled.
However, the control device for a hybrid vehicle described in the above prior art only switches over the operational point of the internal combustion engine and the electric motor based upon the battery remaining amount during vehicle operation. In other words, if the battery remaining amount during vehicle operation becomes lower than the target value, then the operational point of the engine and the motor are switched over to the charge side, while, if the battery remaining amount during vehicle operation becomes higher than the target value, then the operational point of the engine and the motor are switched over to the charge stopped side or the discharge side. Accordingly, there is the problem with this conventional control device for a hybrid vehicle that the fuel consumption is not kept down to its minimum limit in terms of the route to be travelled, since no consideration is accorded to the influence which the road environment and the driving conditions of the route to be travelled exert upon the efficiencies of the engine and the motor.
Accordingly, it is an objective of the present invention to provide a control device and a control method for a hybrid vehicle, which control the internal combustion engine and the electric motor so that the battery remaining amount is brought to a target value, while keeping down the fuel consumption to its minimum limit in terms of the route to be travelled.
The control device for a hybrid vehicle according to the present invention is for controlling a hybrid vehicle which is propelled by either an internal combustion engine or an electric motor or both, and in which electrical power is transferred between the motor and a battery, and includes: a vehicle speed detection device which detects the speed of the vehicle; a drive/brake power command value setting device which sets a drive/brake power command value for the vehicle; an efficiency indication setting device which sets an efficiency indication which indicates the efficiency of utilization of fuel; and an operational point determination device which determines an operational point for the engine and the motor which makes the amount of charge into the battery smaller, the greater is the efficiency indication, based upon the vehicle speed which is detected by the vehicle speed detection device, the drive/brake power command value which is set by the drive/brake power command value setting device, and the efficiency indication which is set by the efficiency indication setting device.
And the control method for a hybrid vehicle according to the present invention is for controlling a hybrid vehicle which is propelled by either an internal combustion engine or an electric motor or both, and in which electrical power is transferred between the motor and a battery, and includes: detecting the speed of the vehicle; setting a drive/brake power command value for the vehicle; setting an efficiency indication which indicates the efficiency of utilization of fuel; and determining an operational point for the engine and the motor, which makes the amount of charge into the battery smaller, the greater is the efficiency indication, based upon the vehicle speed which is detected, and the drive/brake power command value and the efficiency indication which are set.